KR0159180B1 - Steel manufacturing method using converter - Google Patents

Abstract

The present invention is to provide a method for efficiently dephosphorizing, decarburizing or degassing, dephosphorizing and decarburizing molten iron in a converter, wherein the low stirring reaction force is 1.0 Kw / ton or more, and CaO / SiO ₂ in slag after treatment is 0.7-. 2.5, the end point temperature of the treatment was set at 1,200 to 1,450 ° C, and the control was performed so that the T / Fe concentration in the slag after the treatment was 10 to 35% by adjusting the upper feed rate, the lower odor gas flow rate or the upper lance height. Invention.

Description

Steelmaking method

1 is a process flow diagram of the present invention.

2 is a relation between low stirring energy and slag emission ratio.

3 is a relationship between low stirring reaction force and the degree of equilibrium attainment.

4 is a relationship between quicklime consumption unit and dephosphorization amount.

5 is a relationship between the temperature after treatment and the slag basicity to obtain a dephosphorization rate of 80%.

6 is the temperature after dephosphorization, slag basicity and slag discharge rate.

FIG. 7 is a relation between slag emission rate of dephosphorized slag and total keel member unit in order to obtain the same [% P] in the decarburizer blowing.

8 shows the relationship between the sum of total iron and MnO concentrations in slag and (% P) / [% P] after treatment.

9 is a graph showing the change over time of the concentration of [P] in the molten iron.

10 is a relationship between the supply rate of the upper oxygen and the first dephosphorization rate constant.

11 is a relationship between the total concentration of iron oxide and MnO concentration in the decarburized slag and the dolbi development critical decarburized slag temperature.

12 is a graph of the total concentration of iron oxide concentration and MnO concentration of decarburized slag and the dolby developing critical decarburized slag temperature as another example.

13 is a relation between the total iron oxide concentration and the MnO concentration of the decarburized slag and the dolby developing critical decarburized slag temperature as another embodiment.

14 is a rapid discharge state of the dephosphorous slag.

The present invention relates to a converter refining method in a low odor converter in the steel production method. More specifically, desilification and dephosphorization are carried out by the same converter, followed by intermediate elimination, followed by decarburization and further dephosphorization. It is related to the converter reconciliation law to be implemented under the condition.

In recent years, the demand for quality of steel has been increased with the advancement and diversification of the technology used. In response to such demands for high purity steel production, the steelmaking process has attempted to expand the charter preliminary treatment or secondary refining facilities. In particular, in the case of dephosphorization, dephosphorization in the molten iron phase with a low temperature level is efficient, and it has been generally performed to dephosphorize first in the molten iron preliminary treatment process. In this case, the refining vessel includes a topedo car system, a ladle method, or a two converter system separate from a furnace for decarburization, and any of these fluxes, such as CaO and iron oxide, are used. Was added by addition or injection, and nitrogen bubbling or oxygen top blowing was used in combination. For example, in the dephosphorization and degassing method of molten iron disclosed in Japanese Patent Application Laid-Open No. 58-16007, oxygen deodorization is carried out, and then the CaO flux is blown into the molten iron together with a carrier gas and treated with slag basicity of 2.0 or more and iron oxide. A molten iron dephosphorization and degassing method is disclosed in which the molten metal dephosphorization is carried out so that the content is 15% or less, and after that, the blowing of oxygen is stopped and the desulfurizing agent is blown in without treatment of slag. . Also, in the desilification, dephosphorization and deflow method of molten iron disclosed in Japanese Patent Application Laid-Open No. 62-109908, dephosphoric flux containing CaO as a main component is added to the molten iron surface from the beginning of the molten iron preliminary treatment, and iron oxide flux powder is used as a carrier gas during molten iron. A method for desilicon, dephosphorization, and degassing of molten iron which is blown into the molten iron surface by adding oxygen or a solid oxygen source, changing to an alkaline flux after desorption of the silicon, and performing dephosphorization and dehydration in parallel. In addition, the steelmaking method disclosed in Japanese Patent Laid-Open No. 63-195209 uses two upper and lower bleeding furnaces, one using dephosphorization furnace and the other using decarburization furnace. A steelmaking method is disclosed in which a converter slag generated in a decarburization furnace is recycled to a dephosphorization furnace, and the dephosphorization vessel obtained after the molten iron dephosphorization treatment is injected into the decarburization furnace.

As described above, in the primary refining process of molten steel, desilification and dephosphorization processes are carried out in the molten iron phase, and in order to improve the efficiency of decarburization in the converter and to improve productivity, more and more studies have been conducted. It has been put to practical use in steel companies. However, the above methods can achieve a relatively low reached P content level if the process capability of low phosphorus (P) is achieved, but the processing time is long, the heat loss during processing is large, and the time to supply the converter. The process is never satisfactory from the viewpoint of heat margin, because the use of two converters leaves the charter after treatment and reloads into a separate converter to avoid temperature drops. no. Moreover, the recent dephosphorization of all capillaries further lowers the thermal margin in the converter process, and as a result, the degree of freedom of raw materials is lost, and serious problems arise from the viewpoint of active scrap recycling in the future converter.

Compared to the process described above, there is a refining process called a double slag process in which preliminary dephosphorization and decarburization is carried out in one converter. This method is a converter committee of the BOT group in Japan. Page (1969). This process is used to induce dephosphorization by soft blowing refining during the first blow in the converter, and the slab which is de-phosphed to prevent the molten iron from continuously flowing out of the furnace mouth It consists of discharging it, and it continues to the next decarburization refining. However, no technology has been found in this process to improve the refining process or improve slag discharge.

Although the double slag process has a high thermal margin, the cost of the process is high and the refractory consumed is large, as shown below. That is, (1) blast refinement (low stirring power of molten iron in the converter, transfer of carbon [C] of molten iron in the rate determination state) is intentionally induced and the total concentration of iron in the slag (T. Fe Weight%) is maintained at least about 15% or more, it is easy to foam the slag to increase the iron loss. (2) In order to maintain the fluidity of the slag, the blow-off temperature during dephosphorization refining is increased by at least 1,400 ° C by increasing the refining temperature, so that the melting loss of the refractory in the converter slope part is higher. (Iii) is increased. (3) In addition, the dephosphorization efficiency is lowered due to the high blowing-out temperature, and the slag base also has to maintain the CaO / SiO ₂ (a ratio measured in weight%, below) at least 3.0 or more, thereby increasing the flux cost. do. Therefore, this technique is not applied or applied in practice.

In the process described above, decarburizing slag with high CaO concentration in the furnace to recycle decarbonizing slag as dephosphorizing agent and charging the next charge of molten iron is very effective in reducing the flux cost. to be. However, decarburized slag in the converter usually has high oxygen activity. As a result, when the molten iron is charged into the converter, the carbon C in the molten iron explodes with the oxygen in the converter decarburized slag while the converter decarburized slag remains in the molten state, causing the converter to bumping. Problems arise from the so-called dolby phenomenon and the generation of slag bubbles.

The present invention has been made on the basis of the above circumstances, and it is possible to concentrate the pretreatment process to the converter process from a process for which the conventional divisional refining for de-silicon and dephosphorization has been oriented, and thus, it is possible to achieve a significant thermal margin. The aim is to provide an effective refining method that results in improvement.

The gist of the present invention is as follows.

(1) In the converter steelmaking method in which molten iron is charged and refined into a low scavenging converter, the molten gas is charged into a low scavenging furnace, and the low odor gas flow rate is controlled so that the stirring energy is 0.5 Kw / ton or more. CaO / SiO ₂ should be 0.7 to 2.5, and the molten iron is removed by adjusting the amount of flux and the amount of coolant so that the temperature of molten steel after treatment is 1,200 ° C or higher and 1,450 ° C or lower. After discharging more than 60% of the furnace slag by tilting, the stand of the converter is vertical to induce decarburization and the stirring energy (ε) is characterized by controlling the low odor gas flow rate to satisfy the following formula: Converter steel making method.

ε = (2 × 8.314 × 2.3 × 1000 / 22.4 / 60) × (QXT / W)

log [1 + (ρ × g / Pa) × L ₀ ]

= 0.0285 × Q × 10 ³ × T × [log (1 + L ₀ /1.48)/W

From here,

ε: stirring energy (J / S / ton)

Q: Low Odor Gas Flow Rate (Nm ³ / min)

T: Bath temperature (K)

L ₀ : Depth of Bath (m)

W: Bath weight (ton)

ρ: molten iron density (= 7000 Kg / m ³ )

g: acceleration of gravity (= 9.8m / S)

P _A : Atmospheric pressure (= 101325 Pa)

(2) A converter steelmaking method characterized by incorporating oxygen so that the sum of the T.Fe concentration and the MnO concentration in the slag after dephosphorization is 10 to 35% by weight.

(3) A converter steelmaking method in which the oxygen during dephosphorization is depleted of oxygen while maintaining the L / L _O ratio of 0.1 to 0.3.

From here

_{L / L O = L h ·} 10 -3 · exp (-0.78h / L h) L o

^{_{L: L h · 10 -3 ·}} exp (-0.78h / L h): recess depth

L _h : 63.0 × (KQ ₂ / n / d) ^2/3

Q ₂ : Oxygen flow rate (Nm ³ / h)

n: number of nozzles (holes)

d: nozzle diameter (mm)

h: Oxygen uptake height (m)

K: Constant determined by the spray angle of the nozzle

(4) The decarburized slag formed during the decarburization is left in the converter, and the total iron (T · Fe) concentration, MnO concentration, and slag temperature of the slag satisfying the following formula are charged with the molten iron of the next charge, and repetitively. Converter steelmaking method to perform dephosphorization treatment and decarburization treatment.

3.038 × 10 ⁸ × [(% TFe) + (% MnO)] ² × esp (-91400 / Ts + T _M + 546) ≤ 0.1 ---- (1)

From here

(% TFe): Iron oxide weight ratio in decarburized slag (the sum of the iron concentrations in FeO and Fe ₂ O ₃ ) (%)

(% MnO): Manganese oxide weight ratio in decarburized slag (%)

Ts: Temperature of decarburized slag (℃)

T _M : Charging chart temperature (℃)

The present invention consists of a combination of the de-silicon stage and the dephosphorization stage for molten iron during the converter steelmaking. Rapid and thorough slag discharge of dephosphorized slag is essential for the maintenance of current refinery and low toughness steel manufacturing process capacity. That is, when slag is removed during the molten iron treatment process, the following problems are caused. (1) recovery of molten metal during slag discharge, (2) decrease in productivity due to consumption of slag discharge time, (3) high slag removal rate and securing of slag, making P ₂ O ₅ If dephosphorous slag remains in high concentration, even abdominal phenomenon occurs.

The present inventors have undertaken research and development to improve the removal efficiency of molten silicon after molten silicon and dephosphorization by using a converter, and concentrate the molten iron preliminary treatment process in the converter process to significantly improve the heat margin and reduce the flux cost. .

First, the present inventors charge about 290 ton of molten iron using a 300 ton converter having a low converter function on an actual scale, add demineralized quicklime and iron ore, and carry out low agitation while supplying upper oxygen to desilicon. The dephosphorization treatment was carried out, and after the dephosphorization treatment, the blow was stopped, the furnace was tilted to discharge the intermediate slag, and the experiment was carried out continuously to carry out the decarburization. At this time, Si in the molten iron before the treatment was 0.40% on average, P was 0.10% on the average, and the temperature after the dephosphorization was efficiently dephosphorized. Therefore, the target was set at 1,350 占 폚 as is known in the art. As a result, paying attention to the low odor gas stirring power and the composition of the slag after the dephosphorization treatment greatly affects the dephosphorization rate and the slag removal efficiency, it was found that there is an optimum composition that satisfies both.

That is, as shown in Figure 2, the slag emission rate is affected by the low odor gas agitation force, it was found that even in the same slag composition, the slag emission efficiency is rapidly improved to more than 0.5 Kw / Ton. This is because slag foaming level (slag-foaming level) of the slag is increased by the low odor gas and slag discharge is actively performed in the early stage rather than removing the intermediate slag.

Moreover, the present inventors have found that the dephosphorization equation is clearly established in the molten iron as a result of various experiments on dephosphorization. (% Below is all% by weight)

log (% P) / [% P]: 2.5 log [(% T.Fe) + (% MnO)] + 0.0715 [(% CaO) + 0.25 (% MgO) + 7710.2 / T-8.55 + (105.1 / T + 0.0723) [% C) ‥‥‥‥‥‥‥‥ ②

Where (% P) is the phosphorus concentration in the slag and [% P] is the phosphorus concentration in the molten iron. ② The relationship between low stirring reaction force and apparent equilibrium accomplishment degree was investigated.

For the dephosphorization test, an 8-ton converter was specifically used, and about 6 tons of molten iron at an initial temperature of 1,180-1,300 ° C containing 4 to 4.8% C, 0.1 to 0.15% P, and about 0.3% Si was used. Refined for a minute. As a flux, a predetermined amount of CaO was added, and the upper feed rate was 1.1-3.6 Nm ³ / min / ton, and the bottom-blown N ₂ gas ^{3 to} 350 Nm ³ /hr.(0.03 to 3.7 kW / ton) was refined. CaO / SiO in the slag after the treatment was 0.6 to 2.5, and the molten iron temperature was in the range of 1,250 to 1,400 ° C.

In Fig. 3, the relationship between bottom-blowing agitation power and dephosphorization equilibrium attainment (performance (P) / [P] for (P) / [P] obtained from equation ②) is shown. With low stirring reaction force of about 1 kW / ton, dephosphorization reaches approximately equilibrium. Even if the low stirring reaction force increases with the flow rate of the low odor gas, the gas will stir the molten iron if the gas flow rate is too high, and the spitting will increase greatly, so the deep bottom bath depth of the molten iron and the diameter of the low odor twist wire This determines the upper limit of the stirring power.

The stirring power is obtained by the following equation ③.

ε: 0.0285 × Q × 10 ³ × T × log (1 + L ₀ /1.48)/W ‥‥‥‥‥ ③

Where ε is the stirring energy (Watt / TS), Q is the flow rate of low odor gas (Nm ³ / min), T is the bath temperature (K), L ₀ is the bath depth (m), and W is the molten iron (Reference The paper titled Agitation and Metallurgical Reactions in Converters (1980) is the ton of the Japan Science and Technology Association, Steelmaking Section 19, Section 3, Steelmaking Reaction Conference.

4 is a graph showing the relationship between quicklime consumption and dephosphorization when the low stirring reaction force is 1.0 kW / ton or more. As a comparison, the relationship in the conventional process using the top feeder and the molten iron is also shown, and it can be seen from FIG. 4 that the quicklime unit can save about 15 kg / ton compared to the conventional process.

Next, the present inventors investigated the relationship between the molten iron treatment temperature and the slag ratio CaO / SiO ₂ after the treatment (to achieve a dephosphorization rate of 80%) while adjusting the flow rate of the low odor gas to be at least 0.5 kW / ton of agitation power. Is shown in FIG. The present inventors have found that by varying the temperature and the slag discharging his CaO / SiO ₂ ratio after the treatment medium slag subjected to the discharge, were the relationship between the CaO / SiO ₂ ratio and the slag discharge rate in various ways. The result is as shown in FIG.

Furthermore, the following converter work was repeated using the same converter: the molten iron was dephosphorized: the next converter was erected vertically, the molten iron was refined, and the steel thus obtained was removed from the tap hole of the converter. Embarked. Next, the charterer was charged back to the converter leaving the decarburized slag. The slag emission rate and the total amount of CaO in the dephosphorization stage and the decarburization stage in total were investigated. The results are shown in FIG.

In Fig. 7, as much exhaust slag as possible after dephosphorization is necessary to prevent the occurrence of double phosphorus, which reduces the amount of quicklime consumption and improves the recovery of manganese light in the decarburization stage, and the slag emission rate is almost 100%. Even at this level, it is very effective for improving the recovery rate of manganese light. In addition, the amount of quicklime consumed should be maintained at a slag emission rate of 60% or more, so a minimum amount is required. 7 shows that the slag discharge ratio is 60% or more, and the total amount of quicklime used in the dephosphorization step and in the decarburization step can be less than 10 kg / ton by recycling the decarburized slag.

On the other hand, if decarburized slag is not recycled, the sum of consumption in the dephosphorization and decarburization stages is about 15 kg / ton. Therefore, recycling of decarburized slag reduces the consumption of quicklime, which is possible up to about 5 kg / ton.

In addition, as can be seen in FIG. 6, when the slag temperature decreases, solid phase precipitates, the fluidity of the slag deteriorates, and the slag discharge rate is lowered. When the temperature after the treatment is less than 1,200 ° C from FIG. 6, the slag discharge rate does not reach 60% even in the case of CaO / SiO ₂ of the slag after any treatment. Also, even at 1,200 ° C, the slag discharge rate is less than 60% unless the slag CaO / SiO ₂ is 0.7 or more. This is because the viscosity of slag increases when CaO / SiO ₂ becomes too low. Therefore, in view of securing the slag discharge rate, it can be seen that the lower limit of the temperature after the treatment is 1,200 ° C. and the lower limit of the CaO / SiO _{2 for} the slag base is 0.7.

In addition, when the slag base is too high in CaO / SiO ₂ , the slag emission rate is lowered because the melting point of the slag rises and the solid phase precipitates. If the temperature after treatment is 1,450 ° C, slag CaO / SiO ₂ or more is required in order to secure dephosphorization rate of 80% even though total iron is lowered to 5% from FIG. 5, but slag CaO / SiO ₂ is If it exceeds 2.5, the slag emission rate will be less than 60% as shown in FIG. When the temperature increases to 1,500 ° C after treatment, the slag CaO / SiO ₂ required when the total iron (T · Fe) drops to 5% as shown in FIG. 5 is 2.7 or more, but as shown in FIG. With CaO / SiO _2, slag emission rate cannot be as high as 60%. Therefore, the upper limit of the post-treatment temperature is 1450 ℃, the upper limit of the slag CaO / SiO ₂ is found to be 2.5. On the other hand, when the temperature after the treatment is less than 1200 ° C, the slag discharge rate does not reach 60% regardless of the CaO / SiO ₂ ratio in the slag. When the temperature after the refining treatment exceeds 1,450 ° C, the slag discharge rate does not exceed 60% even if the basicity is higher than the required CaO / SiO ₂ ratio. Therefore, in order to obtain high dephosphorization effect and high slag discharge efficiency of 60% or more, the molten iron temperature to be treated must be 1,200 ° C or more and 1,450 ° C or less, and the basic CaO / SiO ₂ ratio in the slag thereafter is 0.7. It should be more than 2.5.

The CaO / SiO ₂ ratio in the slag after treatment is controlled by the amount of flux charged during dephosphorification, and the molten iron temperature after this treatment is also freely controlled by the amount of coolant (scrap and iron ore) charged during dephosphorification. do.

In other words, the required slag discharge rate as well as the predetermined slag discharge rate of 60% were treated with 0.7 to 2.5 in accordance with the molten iron temperature after 1,200 to 1,450 ° C under low stirring reaction force conditions of at least 0.5 kW / ton. The CaO / SiO ₂ ratio can be sufficiently achieved.

Figure 8 also shows the relationship between the sum of the total iron concentrations after gastric treatment and the (% P) / [% P] ratio at the MnO concentration and the molten iron temperature of 1,350 ° C, in which case CaO / SiO ₂ ratio are presented as if to be a 1.0, 1.5 or 2.0. 8 shows that at any CaO / SiO ₂ ratio, if the total iron content and MnO concentration are less than 10%, the (% P) / [% P] ratio drops sharply and if the total iron content exceeds 35% (% P) / [ % P] The ratio does not increase or rather falls off. Here (% P) refers to the concentration of phosphorus (P) in the slag and [% P] refers to the concentration of phosphorus (P) in the molten iron.

This phenomenon occurs for the reasons described below. That is, if the sum of total iron content (T · Fe) and MnO concentration in the slag is less than 10%, the ratio (% P) / [% P] is insufficient due to insufficient oxygen potential as shown in FIG. Falls sharply

If this ratio exceeds 35%, the (% P) / [% P] ratio also drops due to dilution of the base component concentration in the slag.

Therefore, in order to maintain the (% P) / [% P] ratio while maintaining the iron recovery, the sum of the total iron concentration and the MnO concentration after the above treatment is determined by the upper oxygen supply rate and the lower gas flow rate or top-blowing. By adjusting the height of lance), it should be adjusted to more than 10% and less than 35%.

The L / L ₀ ratio (L: depth of the recess of the molten iron / L ₀ : height of oxygen phase lance) is used as an index in the working method as a method of controlling the total iron content after the above treatment by adjusting the supply conditions of the upper oxygen. do.

Here, L / L ₀ ratio is represented by the following formula.

L / L ₀ : L _h exp (-0.78 h / L _h ) / L ₀

L ₀ The depth of the bath (m), h is the height of oxygen phase lance, L is the depth of the molten iron recess,

L _h exp (-0.78 h / L _h ) / L ₀ at L _h is 63.0 × (K / Q ₂ / nd) ^2/3 (where Q ₂ is the flow rate of oxygen Nm ³ / hr.), And also K Is a constant determined by the spray angle of the nozzle).

Basically, as the L / L ₀ ratio decreases, the (% FeO) concentration in the slag increases and the dephosphorization efficiency improves. Specifically, in order to lower the L / L ₀ ratio, it is necessary to raise the lance height. As the lance rises, the secondary combustion ratio in the furnace increases, and the recovery of LDG is lowered or the heat loss is increased in the flue on the slope of the converter. Therefore, increasing the lance height is prohibited. Moreover, as the L / L _O ratio becomes smaller, slag foaming, i.e., foaming, is increased, and slipping that disturbs the converter operation during blowing is more likely to occur. In view of the above problems, the minimum L / L _O ratio is limited to at least 0.1 or more. In addition, as the L / L _O ratio is increased, the total iron content (% T.Fe) in the slag is reduced and the dephosphorization capacity is lowered. Therefore, in order to secure (the total iron concentration is the sum of the MnO concentrations), the efficient dephosphorization is performed by making the content in the slag during dephosphorization refinement at least 10%, so that the L / L _O ratio is limited to 0.3 or less. Needs to be. When controlled to satisfy L / L _O ratio conditions 0.1≤L / _O ≤0.3 L is obtained following advantages:

That is, excessive slopping becomes controllable during dephosphorization; In addition, the [% P] in the molten iron is stably controlled to 0.030% or less to suppress an excessive increase in the second combustion rate of the exhaust gas.

On the other hand, the dephosphorization time can be shortened as the oxygen supply rate increases while the converter is adjusted to low stirring energy, the CaO / SiO ₂ ratio in the slag and the molten iron temperature within the above-mentioned range.

9 shows the change in concentration of [P] in the molten iron under the condition that the slag component and the slag temperature after treatment at different oxygen blowing speeds become almost constant. When oxygen is supplied at a rate of at least 2.5 Nm ³ / min / ton, the treatment time is shortened by about 4 minutes compared to a task where about oxygen is supplied at about 1.1 Nm ³ / min / ton.

10 is a relationship between the oxygen supply rate and the first dephosphorization rate Kp '. FIG. 10 also shows the relationship processed in the conventional steps (1), (2) and (3) with the actual equipment. Although the CaO / SiO ₂ ratio is lowered to 0.6 to 1.1 to reduce the quicklime consumption after refining, the dephosphorization rate increases the oxygen supply rate so that the conventional process (1) using topidoca, or ladle using conventional process (2) A comparable dephosphorization rate constant can be obtained. If the CaO / SiO ₂ ratio is 1.1 to 2.5, the dephosphorization rate constant is about twice that of the conventional process (3) using the same converter.

If the proper dephosphorization meets these conditions in conditions such as the CaO / SiO ₂ ratio in the slag after the refining treatment and the molten iron temperature, the dephosphorization slag can be completely discharged, and the desilicon stage, the dephosphorization stage, and the decarburization stage are thus performed. It is a composite of converters.

That is, after proper dephosphorization, the slag is discharged by tilting the converter, and after slag discharge, the slab is discharged immediately upright, and the flux, such as quicklime and lightly baked dolomite, is reduced to the minimum required slag discharge rate and melt loss in the furnace. Inject according to the state and required [P] concentration, and then decarburize the molten iron by oxygen blowing until the molten iron reaches the required end point [C]. Scrap, iron ore and Mn light are selectively charged to the required [Mn] concentration.

When decarburized slag remains, recirculates in the converter and loads a charter for the next one, the quicklime consumption is severely interrupted, as in FIG. However, even in the same case, C in the molten iron causes vigorous reactions ④, ⑤, and ⑥ with oxygen sources in converter decarburization slag, such as FeO, Fe ₂ O ₃ , MnO, and the like.

FeO + C → Fe + CO ‥‥‥‥‥‥‥‥ ④

Fe ₂ O ₃ + 3C → 2Fe + 3CO ‥‥‥‥‥‥‥‥ ⑤

MnO + C → Mn + CO ‥‥‥‥‥‥‥‥‥ ⑥

This reaction generates a large amount of CO gas, which causes the slag and the charging chart to bounce out of the converter and form a bubble, causing the slag to flow out of the converter. Therefore, when a large amount of CO gas is generated, not only the recovery rate of iron is reduced, but also the work is disturbed.

As shown in equations (4) to (6), the amount of CO gas generated when reacting with FeO, Fe ₂ O ₃ and MnO components in slag increases. Moreover, these reactions increase in speed with the temperature of slag or molten iron. That is, the reaction gets worse as the temperature rises. However, even if the concentration of FeO, Fe ₂ O ₃ or MnO in the slag is high, if the slag temperature is low or the temperature of the molten iron is low, the reaction rate is slowed, so that the boiling or slag in some cases Bubbles do not occur.

As a result of investigating the effects of FeO, Fe ₂ O ₃ , MnO concentration in detail, the inventors of the present invention prevent the boiling and foaming because the slag temperature and the molten iron temperature affect the boiling or slag foaming. In order to do this, it was found that ① must be satisfied. Equation ( ₁ ) means that boiling and slag foaming do not occur when the relationship between the total iron content (the total iron concentration in FeO and Fe ₂ O ₃ ), MnO concentration and slag and molten iron on the left side is 0.1 or less. According to the FeO, Fe ₂ O ₃ , MnO concentration in the slag ① After selecting the slag temperature or the molten iron temperature so that the left side of the formula is 0.1 or less, the charging of molten iron can prevent boiling and slag foaming. On the other hand, on the basis of the slag temperature and the molten iron temperature, boiling and slag foaming occurs even when the molten iron is charged by adjusting the total iron (T.Fe) concentration and the MnO concentration in the slag to satisfy the relationship of the equation (1). The phenomenon can be prevented.

In addition, the molten iron may wait to be charged until the sum of iron oxide and manganese oxide concentrations in the decarburized slag and the temperature of the decarburized slag determined by the molten iron temperature of the next charge is satisfied to satisfy the equation, but a coolant such as CaCO ₃ , coke or smoke A mixture of a deoxidizing agent such as anthracite and a coolant, which is absent, may be forcibly made to satisfy the condition (1).

For example, when using CaCO ₃ as a coolant, CaCO ₃ is decomposed, but CaO and CO ₂ waro, the decomposition reaction is an endothermic reaction to go down, so the decarburization slag its temperature, can not satisfy the condition of equation ① foregoing in a short time. In addition, since CaO after decomposition plays a role as a flux of the dephosphorization reaction, the dephosphorization flux (dephosphorization flux) of the dephosphorization group can be reduced, which is very useful.

The sum of iron oxide and manganese oxide concentrations in the decarburized slag can be analyzed quickly when the slag sample is collected or obtained by calculating the total relationship between the carbon concentration in molten steel and the iron oxide and manganese oxide concentration in the decarburized slag, It calculates from the analysis result of the carbon concentration in molten steel after decarburization. In addition, the temperature of decarburized slag is measured with a radiation thermometer.

1 is a schematic of the overall process.

The present invention has been described above as a case of refining molten iron that has first been avitalized outside the converter. When a high degree of preliminary dehydration is not required, the molten iron can be degassed before dephosphorization as described above.

That is, at least two or more substances selected from CaO, Na ₂ CO ₃ , and Mg as the defluxing flux are charged by the top loading or the low spray injection, followed by a deflow treatment in a short period of 2 to 5 minutes. The dephosphorization treatment described above is then performed.

Since 40 to 60% of S in the slag is evaporated or degassed, 30 to 50% of [S] in the molten iron is degassed at the initial stage with dephosphorization to allow adjustment of the flux amount.

In addition, when discharging the slag by tilting the conduction, the slag is preferably turned over in one minute (if fast) and the slag is scattered by the anti-slag plate in front of the converter as shown in FIG. It prevents you from becoming.

The present invention will be described in detail by way of examples. However, L / L _O during dephosphorization treatment in Examples below were carried out in 0.2.

Example 1

After charging about 6 tons of molten iron preliminarily decanted into an 8 ton test furnace with low odor function and adjusting the flux and scrap loading, it was demineralized for about 8 minutes, and the CaO / SiO ₂ ratio in the slag after refining was 1.5 ( CaO: 35% by weight, SiO ₂ : 23% by weight, T · Fe: 14% by weight, MnO: 7% by weight). The molten steel temperature after the treatment was maintained at 1,200 ° C to 1,450 ° C (see FIGS. 5 to 7). On the other hand, the flow rate of the low odor gas was controlled, and the stirring energy for controlling the gas flow rate was 0.5 kW / ton or more (see FIG. 3). The test furnace was then tilted to discharge the extra slag over about 3 minutes. Thereafter, the furnace was erected vertically and immediately decarburized for about 9 minutes and then tapped out of the molten steel. Of course, the slag discharge rate during the dephosphorization treatment was maintained at 60% or more in order to reduce CaO raw units.

Table 1 shows the specific conditions, chemical composition of molten steel and temperature change of steel.

[P] of molten iron after dephosphorization was 0.025%, and [P] of molten steel after decarburization was 0.019%. The total unit of raw lime added to dephosphorization and decarburization in the preliminary dehydration and converter was 20 kg / ton, equivalent. Compared to the average clean stone member unit of 34 Kg / ton in the conventional method (melting degassing, dephosphorization + converter decarburization) for obtaining a refining effect, the present invention enables a significant reduction in raw units.

In addition, as shown in FIG. 7, when the slag discharge rate is 60% or more, the total quickener member unit is reduced to 10 kg / ton or less, which is further reduced when the repetitive work is repeated. Since the slag generated during decarburization is used for the dephosphorization treatment of the next charge, the amount of quicklime in the dephosphor is further reduced.

As a result, the application of the dephosphorization working conditions of the present invention resulted in a high slag discharge rate and a high dephosphorization effect.

Example 2

Charge 6 tons of molten iron preliminarily preliminarily into the 8 ton test furnace with low odor function, and adjust the amount of molten iron in the flux and the amount of scrap in the molten iron for approximately 8 minutes to reduce the CaO / SiO ratio in the slag after treatment. It was made to fall within -2.5, and the molten steel temperature was set to 1,200-1,450 degreeC. On the other hand, the stirring energy became at least 0.5 kW / ton due to the controlled flow rate of low odor gas. This converter was then tilted and the intermediate slag was discharged for about 3 minutes.

Also in Example 2, the result shown by 3rd, 5-7 degree was obtained like Example 1.

Next, the converter was upright, and decarburization was carried out in particular for about 9 minutes. Then tapping to go out. The scrap loading amount was changed in order to run 4 charters of the molten iron.

Table 2 shows the conditions such as chemical composition, temperature, etc. of each tea.

As can be seen here, a large amount of scrap up to about 17% can also be charged when it has a high thermal margin as in the process of the present invention. In the conventional method, dephosphorization and decarburization are carried out in topidoca and converter. In this case, the amount of scrap charged can be compared with only about 7%.

Moreover, it can be seen from the result that when the [Si] in the molten iron is increased, the molten iron increases the amount of slag formed in the dephosphorization step so that it becomes dephosphorized at low basicity. And as a result, the consumption unit of quicklime is not increased very much. Even if the [Si] in the core is increased, the operation is stable without large slipping due to low basicity and low temperature. This work is performed at a scrap rate of 25% using a molten iron having a content of [Si] of 1%.

Example 3

About 6 tonnes of preliminary molten iron was charged into the 8 ton test furnace with low odor function, and the amount of flux and scrap was adjusted to de-intake for about 8 minutes, and the CaO / SiO ratio in the slag after refining was 0.7-2.5. . Moreover, the molten iron temperature after processing became 1,200 degreeC-1,450 degreeC. On the other hand, the flow rate of the low odor gas was controlled, and the stirring energy required at least 0.5 Kw / ton or more. Next, the test furnace was tilted to discharge the intermediate slag over about 3 minutes, and then the furnace was vertically set up, and immediately decarburization was performed for about 9 minutes, and tapping was carried out by tapping molten steel. Also in Example 3, the result shown by 3, 5-7 degree was obtained like Example 1.

Table 3 shows specific conditions such as chemical composition and temperature change of molten steel.

In the initial stage, [S] of the molten iron decreased from 0.030% to 0.010% after degassing, to 0.015% after dephosphorization and to 0.014% after decarburization. Therefore, it was found that the molten iron could sufficiently drain to the level of ordinary steel.

Example 4

As an example, 290-300 tonnes of molten iron are charged into a 300-ton bottom blower with a bottom-blowing tuyere in the Roger, CO from the low-coater and O from an upper-blowing lance. Was applied to each of the present invention and the results are shown in Table 4.

Comparative Examples 1-3 are examples in which the slag base group after the dephosphorization treatment is 2.0 or more or refined with a small stirring force, and Examples 4 to 7 are carried out according to the present invention. The basicity adjustment could be easily performed by adding the amount of quicklime from the amount of SiO generated from the molten iron concentration before treatment and the amount of SiO in the residual slag.

As can be seen from the results in this example, by applying the present invention, it becomes possible to significantly improve the intermediate slag discharge rate after dephosphorization treatment compared to the conventional method, and in the decarburization process continuously performed after slag discharge. Since the rephosphorization of can be suppressed, there is an advantage in that even one furnace can sufficiently perform desilicon, dephosphorization and decarburization.

The operating conditions of the data described in Table 4 above were as follows.

(1) The stirring energy, the slag base after the treatment, the CaO / SiO, the molten steel temperature after the treatment and the like were the same as described in Examples 1-3. (See also paragraphs 5-7)

(2) Stirring energy was as shown in Figure 3,

(3) Iron oxide concentration and Mn concentration of slag were the same as the result shown in FIG.

As shown in the above table, it can be seen that the performance value of T · Fe + MnO is in the range of 10.7-15.8 wt%.

Example 5

Using a 300-ton converter, the decarburized slag formed in the previous decarburization step was not discharged, but the molten iron of the next chaze was charged thereto. Next, the slag was reused as dephosphorization flux to carry out the converter work.

The decarburized slag remaining in the furnace has a temperature that is the molten iron temperature, and when the decarburized slag has a concentration (% T.Fe + MnO) that is the sum of the total iron content of the decarburized slag and manganese oxide

(1) The conditions of the formula were satisfied, and 300 tonnes of molten iron were charged therein with 1) 1,290 to 1,310 ° C, 2) 1,340 to 1,360 ° C, or 3) 1,390 to 1,410 ° C.

In addition, the chemical composition of molten iron was as follows. : The molten iron [C] concentration was 4.5 to 4.8%, the molten silicon [Si] concentration was 0.39 to 0.41%, the molten iron [P] concentration was 0.099 to 0.103%, and the amount of decarburized slag remaining in the converter was about 30 kg / ton. In addition, the molten iron was also charged for comparison even if it did not satisfy the condition. Boiling, i.e., dolby or rapid foaming, does not occur after charging, and FIGS. 11 to 13 show the molten iron temperatures.

The oblique part in FIGS. 11-13 is a range which satisfy | fills the conditions of (1) formula. In addition, O mark shows the case where Dolby phenomenon and slag foaming did not generate | occur | produce when molten iron was charged, and X mark shows the case where it occurred. On the other hand, when the charter was charged while satisfying the conditions of ①, neither Dolby phenomenon nor slag foaming occurred and it did not interfere with the operation.

Moreover, when the comparative example was implemented, the decarburized slag was discharged | emitted from the converter once here. The slag was crushed and used as molten flux for molten iron. However, in the present invention, the scrap ratio was increased by 5% on average, and the thermal margin was increased in the comparative example test. Subsequently, dephosphorization was performed. The results were as follows. Ie, decarburized slag was reused as deinflux; CaO composition in decarburized slag was effectively used for dephosphorization; The CaO consumption units to be charged in the dephosphorization stage were reduced compared to the case where decarburized slag for the dephosphorization stage was not reused.

It can be seen that the present invention has the following effects from the above-described embodiment.

(1) The conventional out-of-conduction charter de-phosphorization or degassing and de-induction processes can be integrated into the converter, and the fixed cost can be greatly reduced.

(2) Flux consumption unit can be reduced, reducing variable costs.

(3) Improvement of heat margin due to process intensity 1) Improvement of melting ability of scrap 2) Improvement of molten steel recovery due to increase of iron ore reduction amount 3) Reduction of flux cost by replacing quicklime with limestone You can enjoy Merritt.

(4) The total consumption of slag from the converter refining process can be reduced to about 2/3 of the conventional level, thereby reducing the consumption unit of flux.

Claims (4)

In the converter steelmaking method in which molten iron is charged and refined into a low scavenging furnace, the molten gas is charged into a low smelting furnace and the low odor gas flow is controlled so that the stirring energy is 0.5 Kw / ton or more, while CaO / SiO in the slag after treatment ₂ is 0.7 to 2.5, and the molten iron is dephosphorized by adjusting the input flux amount and the input coolant amount so that the temperature of the molten steel after treatment is 1,200 ° C or higher and 1,450 ° C or lower, and once refining is stopped, tilting the converter. After discharging more than 60% of the slag in the furnace, the stand of the converter vertically to induce decarburization, the stirring energy (ε) is a converter steelmaking method characterized in that to control the low odor gas flow rate to satisfy the following formula . ε = (2 × 8.314 × 2.3 × 1000 / 22.4 / 60) × (QXT / W) log [1+ (ρ × g / pa) × L _O ] = 0.0285 × Q × 10 ³ × T × (log (1 + L _O /1.48)/W From here, ε: stirring energy (J / S / ton) Q: Low Odor Gas Flow Rate (Nm ³ / min) T: Bath temperature (K) L _O : Depth of bath (m) W: molten metal weight (ton) ρ: molten iron density (= 7000 Kg / m ³ ) g: gravitational acceleration (= 9.8m / S) P _A : Atmospheric pressure (= 101325 P _A ) The converter steelmaking method according to claim 1, wherein the sum of total iron content (T · Fe) and MnO concentration in the slag after dephosphorization is configured to be 10 to 35% of the slag weight after dephosphorization. The method of claim 1, wherein the oxygen is a converter steelmaking method to deodorize the oxygen while maintaining the L / L _O ratio of 0.1 ~ 0.3. From here _{L / L O = L h ·} 10 -3 · exp (-0.78h / L h) L o ^{_{L: L h · 10 -3 ·}} exp (-0.78h / L h): recess depth L _h : 63.0 × (KQ ₂ / n / d) ^2/3 Q ₂ : Oxygen flow rate (Nm ³ / h) n: number of nozzles (holes) d: nozzle diameter (mm) h: Oxygen uptake height (m) K: Constant determined by the spray angle of the nozzle The decarburized slag formed during the decarburization is left in the converter, and the total iron (T · Fe) concentration, the MnO concentration, and the slag temperature of the slag satisfying the following equation are charged with the molten iron of the next charge. A converter steelmaking method in which dephosphorization treatment and decarburization treatment are repeatedly performed. 3.038 × 10 ⁸ × [(% T · Fe) + (% MnO)] ² × exp (−91400 / Ts + T _M +546) ≦ 0.1... … (One) From here (% TFe): Iron oxide weight ratio in decarburized slag (Sum of iron concentration in FeO and Fe ₂ O ₃ ) (%) (% Mn O): Manganese oxide weight ratio in decarburized slag (%) Ts: Temperature of decarburized slag (℃) T _M : Charging chart temperature (℃)